It covers 321 km2 (124 sq mi) at an elevation range of 850–1,250 m (2,790–4,100 ft) in the Nilgiri District and shares boundaries with the states of Karnataka and Kerala.

Traffic on three public roads passing through the national park has caused significant roadkills of mammals, reptiles and amphibians.

[9] The original national park area together with a surrounding buffer zone of 367.59 km2 (141.93 sq mi) was designated as the Mudumalai Tiger Reserve.

[16] Mudumalai National Park receives about 1,420 mm (56 in) rainfall annually, most of it during the southwest monsoon season from June to September.

[22] An exceptionally large arjun tree (Terminalia arjuna) with a height of 32 m (105 ft) and a girth of 8.45 m (27.7 ft) was detected in the Moyar River valley in 2019; it was used by white-rumped vulture (Gyps bengalensis), brown fish owl (Ketupa zeylonensis), spot-bellied eagle-owl (Bubo nipalensis), crested honey buzzard (Pernis ptilorhynchus), changeable hawk-eagle (Nisaetus cirrhatus) and shikra (Accipiter badius) for roosting.

[12] Scat of sloth bear (Melursus ursinus) collected along forest roads and animal trails contained remains of 18 plant species with golden shower (Cassia fistula), Indian plum (Zizyphus mauritiana) and clammy cherry (Cordia obliqua) forming the bulk of its diet apart from fungus-growing termites (Odontotermes), fire ants and honey bees.

The gaur (Bos gaurus) is the largest ungulate in the park, with herds of up to 42 individuals that frequent foremost grasslands in the vicinity of water sources.

[36] A troop in the Moyar River valley foraged on leaves, flowers and fruits of several tree and shrub species including tamarind (Tamarindus indica), banyan fig (Ficus benghalensis), wild jujube (Ziziphus oenoplia), neem (Azadirachta indica), kaayam (Memecylon edule) and indigoberry (Randia malabarica), but also consumed herbs, crickets and grasshoppers.

[37] The range of the Indian giant squirrel (Ratufa indica) is continuous in the national park's moist deciduous forest; in the drier eastern part, it inhabits foremost riverine habitat with contiguous canopy.

It builds nests in trees with a mean canopy height of 10.6 m (35 ft) and feeds on 25 plant species including teak, Indian laurel and Grewia tiliifolia.

[40] Birds observed from 1994 to 1996 comprised 266 species; the 213 resident ones include Malabar grey hornbill (Ocyceros griseus), Indian grey hornbill (O. birostris), Indian peafowl (Pavo cristatus), Bonelli's eagle (Aquila fasciata), crested serpent eagle (Spilornis cheela), black eagle (Ictinaetus malaiensis), besra (Accipiter virgatus) and crested goshawk (A. trivirgatus), white-rumped shama (Copsychus malabaricus), Indian roller (Coracias benghalensis), greater flameback (Chrysocolaptes guttacristatus) and white-naped woodpecker (C. festivus), black-rumped flameback (Dinopium benghalense), white-bellied woodpecker (Dryocopus javensis), heart-spotted woodpecker (Hemicircus canente), rufous woodpecker (Micropternus brachyurus), greater racket-tailed drongo (Dicrurus paradiseus), grey-bellied cuckoo (Cacomantis passerinus) and Indian cuckoo (Cuculus micropterus), coppersmith barbet (Psilopogon haemacephalus), white-cheeked barbet (P. viridis) and brown-headed barbet (P. zeylanicus), grey francolin (Ortygornis pondicerianus), speckled piculet (Picumnus innominatus), Indian pond heron (Ardeola grayii), white-throated kingfisher (Halcyon smyrnensis), blue-winged parakeet (Psittacula columboides), Nilgiri wood pigeon (Columba elphinstonii), common emerald dove (Chalcophaps indica), yellow-footed pigeon (Treron phoenicoptera), red spurfowl (Galloperdix spadicea) and grey junglefowl (Gallus sonneratii), painted bush quail (Perdicula erythrorhyncha), crimson-backed sunbird (Leptocoma minima), Loten's sunbird (Cinnyris lotenius), forest wagtail (Dendronanthus indicus), white-browed wagtail (Motacilla maderaspatensis) black-and-orange flycatcher (Ficedula nigrorufa), Eurasian golden oriole (Oriolus oriolus) and black-hooded oriole (O.

[41] December to March is the breeding season of yellow-crowned woodpecker (Leiopicus mahrattensis), streak-throated woodpecker (Picus xanthopygaeus), yellow-throated sparrow (Gymnoris xanthocollis), blue-bearded bee-eater (Nyctyornis atherton), Indian robin (Saxicoloides fulicatus), scaly-breasted munia (Lonchura punctulata) and white-rumped munia (L.

[22] Spot-bellied eagle-owl, Oriental scops owl (Otus sunia), brown boobook (Ninox scutulata) and jungle owlet (Glaucidium radiatum) are known night birds in the region.

[44] Sightings of migrating birds include booted eagle (Hieraaetus pennatus), rufous-bellied eagle (Lophotriorchis kienerii), Eurasian sparrowhawk (Accipiter nisus), common buzzard (Buteo buteo), western marsh harrier (Circus aeruginosus) and pallid harrier (C. macrourus), cotton pygmy goose (Nettapus coromandelianus), knob-billed duck (Sarkidiornis melanotos), northern pintail (Anas acuta) and rosy starling (Pastor roseus).

[48] Small reptiles recorded in Mudumalai National Park comprise striped coral snake (Calliophis nigrescens), Elliot's forest lizard (Monilesaurus ellioti), Jerdon's day gecko (Cnemaspis jerdonii), Goan day gecko (C. indraneildasii) and Beddome's ground skink (Kaestlea beddomii).

[49] A dead Bibron's coral snake (Calliophis bibroni) was discovered on the road in the Theppakadu area at an elevation of 894 m (2,933 ft) in August 2013, the first record since 1874.

[51] The Moyar River and tributaries harbour 38 fish species, including Nilgiri mystus (Hemibagrus punctatus), Puntius mudumalaiensis, Puntius melanostigma, reba carp (Cirrhinus reba), common carp (Cyprinus carpio), Deccan mahseer (Tor khudree), Malabar baril (Barilius gatensis), mullya garra (Garra mullya), zig-zag eel (Mastacembelus armatus) and bullseye snakehead (Channa marulius).

[53] Between December 2006 and November 2007, 101 amphibians and 78 reptiles became roadkills on a 6 km (3.7 mi) stretch of the national highway passing through the park including Indirana frogs, Indian skipper frog (Euphlyctis cyanophlyctis), bronzed frog (Indosylvirana temporalis), pigmy wrinkled frog (Nyctibatrachus beddomii), Asian common toad (Duttaphrynus melanostictus), common green forest lizard (Calotes calotes), Blanford's rock agama (Psammophilus blanfordanus), Mysore day gecko (Cnemaspis mysoriensis), bronze grass skink (Eutropis macularia), green keelback (Rhabdophis plumbicolor), trinket snake (Coelognathus helena), Russell's viper (Daboia russelii), common krait (Bungarus caeruleus) and hump-nosed viper (Hypnale hypnale).

[54] Between January 2014 and December 2016, 497 Indian palm squirrels (Funambulus palmarum) were found killed in traffic collisions on a 40 km (25 mi) long stretch of a state highway passing through the park.